1. Field of the Invention:
The invention relates to a flexible sensor tube for determining a concentration curve of a medium along a path. The invention also relates to a method for determining the concentration curve of the medium along the path with a flexible sensor tube of that kind. Such a flexible sensor tube can be used for monitoring pipes, tanks or garbage dumps.
A flexible sensor tube and an apparatus for operating it are known from German Patent DE 24 31 907 C3, corresponding to U.S. Pat. No. 3,977,233. With that flexible sensor tube and apparatus it can be ascertained whether or not a medium is present in the vicinity of the flexible sensor tube. In addition, it is possible to determine a point on the flexible sensor tube where the medium encounters the flexible sensor tube. A concentration curve over the length of the flexible sensor tube can be produced. The flexible tube is permeable to the medium to be detected. A pump is disposed at one end of the flexible tube. With the aid of the pump, individual volumes of a conveying medium can be conveyed through the flexible tube one after the other at intervals of time. A suitable conveying medium is a gas, particularly air. In that way the flow passes through the flexible tube at regular intervals of time, that is to say with a constant frequency, for a conveying period in each case. A sensor being sensitive to the medium to be detected is provided at the other end of the flexible tube. The pump remains switched off between each two conveying periods for a diffusion period, which is distinctly longer than a conveying period. If a medium which is to be detected comes into the vicinity of the flexible tube, it penetrates into the latter within a diffusion period of that kind and is brought to the sensor within a conveying period by the next volume of conveying medium. Since the conveying medium flows at a known speed, the point at which the medium has passed into the flexible tube between two pumping operations can be accurately determined from the difference between the time when the pump is switched on and the time when the sensor responds. In addition, the amount of medium that has penetrated can be determined.
From European Application 0 175 219 A1, corresponding to U.S. Pat. No. 4,735,095, a pipe is known which can be used as a flexible sensor tube in the manner described. That pipe contains a tubular pipe which is impermeable to the medium to be detected and which has individual apertures. That pipe of impermeable material can be surrounded by a pipe of a permeable material. It is also possible for only the apertures in the pipe of impermeable material to be closed by a permeable material. During its conveyance through the pipe the medium which has diffused into the latter from outside can only diffuse out of the pipe again to a very limited extent while it is being conveyed through the pipe, since the inner wall surface of the pipe is for the most part impermeable. The production of a hollow pipe of that kind is very expensive, since the impermeable pipe has to be provided with a number of apertures, particularly bores.
2. Summary of the Invention:
It is accordingly an object of the invention to provide a flexible sensor tube and a method of determining a concentration curve of a medium along a path with the flexible sensor tube, which overcome the hereinafore-mentioned disadvantages of the heretofore-known products and methods of this general type, and in which the flexible sensor tube works reliably in the determination of the concentration curve of the medium along the path and additionally can be produced quickly and in a simple manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a flexible sensor tube for determining a concentration curve of a medium along a path, comprising a flexible tube being formed of a material having good permeability to a medium and having an inner surface; and a thin coating completely covering the inner surface and being formed of a material having poor permeability to the medium.
The advantage which is thereby achieved is that the medium reaching the flexible sensor tube from the outside always encounters a material which has good permeability and can therefore easily penetrate into the material. From that point an amount of medium sufficient for detection overcomes the thin coating of material having poor permeability and passes into the interior of the flexible sensor tube. From there the medium is practically unable to pass out of the flexible sensor tube through the wall of the latter. That is due to the fact that the thin coating of the material having poor permeability to the medium bounds or borders the interior space of the flexible sensor tube. Due to the relatively fast conveyance of the medium in the flexible sensor tube, the medium has no time to penetrate again into the thin coating to any noteworthy extent. Consequently, it cannot pass to the outside from the flexible tube to any noteworthy extent. It is thereby ensured that the measurements being made are not falsified.
The material having poor permeability absorbs vapor molecules only to a very slight extent. In addition, it has low affinity for nonpolar molecules, which, for example, include hydrocarbons. It is precisely such substances that frequently have to be detected.
The advantage which is therefore achieved is that on its path from the outside into the flexible sensor tube the medium can overcome the thin coating within the diffusion period, whereas from the interior of the flexible sensor tube it can scarcely penetrate into the coating within the conveying period, so that it remains trapped in the flexible sensor tube. Due to the fact that practically no medium which has penetrated into the flexible sensor tube is lost during its conveyance, the concentration curve can be determined very accurately.
In particular, the flexible sensor tube in question achieves the advantage of permitting the tube to be produced quickly and simply, since no apertures have to be formed in it.
The coating of the flexible sensor tube can be effected by processes of precipitation from a gas phase, lacquering processes or immersion processes. It is also possible to insert an inner flexible tube, which is subsequently pressed against the inner surface by expansion of the inner tube.
In accordance with another feature of the invention, the thickness of the coating of material having poor permeability amounts, for example, to between 100 .mu.m and 800 .mu.m. Such a thin coating is not a significant obstacle for a large amount of the medium which has penetrated into the relatively thick wall of the flexible sensor tube of the material having good permeability. Nevertheless, it prevents the penetration of the medium from the inside into the wall of the flexible sensor tube.
With the objects of the invention in view, there is also provided a flexible sensor tube for determining a concentration curve of a medium along a path, comprising a flexible tube being formed of a material having good permeability to a medium and having an inner surface and a longitudinal direction; and another material coating the inner surface and being poorly permeable or impermeable to the medium, defining a narrow strip extending in the longitudinal direction of the flexible tube and being left free of the other material.
The advantage which is thereby gained is that at the uncoated strip a particularly large amount of medium can pass from the outside into the flexible sensor tube. That is assisted by the fact that in the material having good permeability the medium can pass to the strip having particularly good permeability, even if it should have penetrated at a different point. However, the medium which has arrived in the flexible sensor tube can scarcely leave the latter, because the strip having good permeability is very small in comparison with the entire inner surface of the flexible sensor tube. Even less medium can leave the flexible sensor tube again if, instead of being of material having poor permeability, the coating is formed of impermeable material. Only the free strip is then available.
In accordance with a further feature of the invention, the strip has, for example, a width of 0.1 mm to 2 mm. With such a narrow strip the advantage which is gained is that almost no medium can leave the flexible tube again.
In accordance with an added feature of the invention, while leaving the strip free, the flexible tube is, for example, coated with a coating of a thickness between 1 mm and 5 mm. That coating contributes toward the mechanical stability of the flexible sensor tube.
The flexible tubes of the first and second embodiments can, for example, have a circular or polygonal, for example rectangular, cross-section.
With the objects of the invention in view, there is additionally provided a flexible sensor tube for determining a concentration curve of a medium along a path, comprising a band being formed of a material being poorly permeable or impermeable to a medium, being bent into the shape of a trough, having a slot-like aperture being left free therein and having a longitudinal direction; and a strip closing the slot-like aperture, extending in the longitudinal direction of the band and being formed of a material having good permeability to the medium.
In this embodiment also the penetrated medium is to a large extent trapped in the flexible sensor tube.
In accordance with an additional feature of the invention, the slot-like aperture has, for example, a width between 0.1 mm and 2 mm. In accordance with yet another feature of the invention, the band may, for example, be 1 mm to 5 mm in thickness. The mechanical stability of the flexible sensor tube is thereby ensured.
The band being bent into the shape of a trough or a channel may, for example, have a circular or polygonal cross-section.
All of the flexible sensor tubes according to the invention are in particular distinguished by the fact that they can be produced quickly in a simple manner. Complete coating and also coating with a strip being left free can easily be achieved. A flexible sensor tube having a strip being formed of a different material than the remainder of the tube is also easy to produce.
If the flexible sensor tube has a polygonal cross-section with two surfaces being parallel to one another, it can be inserted particularly well into a space which is to be monitored and which is bounded by two parallel seals, for example sheets. The parallel surfaces of the flexible sensor tube in that case can lie against the seals, so that the flexible sensor tube serves as a spacer between the seals.
Seals of that kind may be component parts of a device which is known from German Published, Non-Prosecuted Application DE 41 09 520 A1, corresponding to U.S. Pat. No. 5,215,409, for sealing and monitoring a volume, which may be a garbage dump.
In accordance with yet a further feature of the invention, the material having good permeability to the medium may, for example, be ethylene vinyl acetate (EVA).
In accordance with yet an added feature of the invention, the material having poor permeability to the medium is polyvinyl chloride (PVC).
With the objects of the invention in view, there is additionally provided a method for determining a concentration curve of a medium along a path with a flexible sensor tube, which comprises feeding a conveying medium into the beginning of the flexible sensor tube at intervals of time; and monitoring the conveying medium arriving at the end of the flexible sensor tube for an admixture of the medium to be detected.
Reliable determination of the concentration curve is possible through the use of one of the variants of the flexible sensor tube.
The flexible sensor tube according to the invention in particular gains the advantage of permitting the flexible sensor tube to be produced quickly and simply. The first and second variants are formed of a homogeneous, internally coated flexible tube which is simple to produce. The third variant, which has an insert of a different material in the longitudinal direction, is also easy to produce. For that purpose only one band has to be bent into the shape of a trough or a C-shape, whereupon the remaining gap is closed with the other material.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a flexible sensor tube and a method of determining a concentration curve of a medium along a path with the flexible sensor tube, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.